1. Field of the Invention
The present invention is related to a method for controlling the activation of a set of disk drive motors which can be used in a magnetic disk device, an optical disk device, and the like, and more particularly to a method for a motor activation control in which a motor activation start time delay is set at any desired value in the form of a command from a host control device and is applicable to any kind of subsystem in a flexible way.
2. Description of the Related Art
In a magnetic disk device, for example, a motor such as a spindle motor is used as is standard in the art. To activate the motor, the following two methods are available.
1: Letting the magnetic disk device itself start activating the motor after providing electric power to the magnetic disk device.
In this method, in the case where a plurality of magnetic disk devices are disposed in a magnetic disk subsystem, upon simultaneous supply of electric power to the plurality of magnetic disk devices, as many motor starting currents as the number of the magnetic disk devices are superimposed, thereby an extremely large load is created. There are two methods to avoid this as described below.
2-a: Delaying activation of the motor of each magnetic disk device by a predetermined time delay which is determined in accordance with the device number set value of the magnetic disk device.
1-b: Monitoring and controlling, in a power source unit of the magnetic disk subsystem, the time to supply electric power to the plurality of magnetic disk devices.
2: Letting the magnetic disk device start activating the motor which is mounted therein in response to a motor start command which is received from a host device, that is, a magnetic disk control device.
In this method, in the case where a plurality of magnetic disk devices are disposed in a magnetic disk subsystem, if the plurality of magnetic disk devices receive the motor start command at the same time, as many motor starting currents as the number of the magnetic disk devices are superimposed, thereby an extremely large load is created. As a method of preventing this, the following method is available.
2-a: Letting the magnetic disk control device supply the motor start command to the plurality of magnetic disk devices while monitoring an interval for supplying the motor start commands.
The conventional technique as described above has the following problems.
(1) In the case where a plurality of magnetic disk devices are disposed in a magnetic disk subsystem, if the motors of the plurality of magnetic disk devices are activated at the same time, as many motor staring currents as the number of the magnetic disk devices are superimposed, thereby an extremely large load is created.
Although the methods 1-a, 1-b and 2-a are available as solutions of the problem, any one of these methods must be designed exclusively for a particular subsystem, and therefore, is not flexible. Hence, these methods prohibit use of the magnetic disk devices or the power source unit of some manufacturers in some cases.
(2) As to the methods 1-a and 1-b, since motor activation start time delays are fixed in the magnetic disk devices, if the motor activation start time delays become inappropriate due to provision of an additional magnetic disk device or a change in the capacity of the power source unit, these methods cannot deal with the change in the situation.
(3) In the method 2-a, at every activation of the magnet disk devices, it is necessary to monitor the interval for supplying the motor start commands which are to be given to the respective magnetic disk devices all through the activation. Hence, while the interval for supplying the motor start commands is monitored, the magnetic disk control device cannot perform its other functions.